Lifetime bone cancer dose-response relationships in beagles and people from skeletal burdens of 226Ra and 90Sr.

The life-time tumor dose-response relationships observed in beagles injected with 226Ra or fed 90Sr at the University of California, Davis, provide a basis for understanding the induction of bone cancer for these bone-seeking radionuclides and for scaling to people. In these studies 385 dogs were exposed to graded dosage levels of 90Sr and 243 dogs were exposed to graded dosage levels of 226Ra with a total of 159 unexposed controls. The results show different dose-response relationships for bone cancer for the two radionuclides based upon the gravimetric average dose rates and cumulative doses to bone. These relationships were found to be well represented by three-dimensional log-normal dose-response surfaces that yield risk as a function of average dose-rate and time after beginning of exposure. All dose-rates suggested a 100% risk at some later time post-exposure but the time required to reach a given level of risk was long for low dose rates so that there exists a practical threshold in that at lower dose rates individuals may die spontaneously from causes associated with natural aging prior to the expected appearance of radiogenic cancer. The risks to people at various 226Ra body burdens (average skeletal dose rates) are estimated based on the model.